To flow liquids in pipes, energy must be expended to overcome frictional losses. This energy is extracted from the liquid pressure, which decreases along the pipe in the direction of flow. For a fixed pipe diameter, these pressure losses increase with increasing flow rate until a maximum is reached when the pressure drop along the pipe equals the maximal supply pressure dictated by the pumping device or pipe strength. When flow in the pipe is turbulent (flow Reynolds number=means fluid velocity.times.pipe diameter.div.fluid kinematic viscosity greater than about 2000) this maximum flow rate can be increased by the addition of small amounts of certain high molecular weight linear polymers to the liquid. These polymers interact with the turbulent flow processes and reduce frictional pressure losses such that the pressure drop for a given flow rate is less, or the maximum flow rate for a given pressure drop is larger. This phenomenon is commonly called drag reduction. It has been used in commercial oil pipelines, fire hoses and storm sewers to increase the flow capacities of existing systems. It can also be used to reduce supply pressures, pumping costs, and/or pipe diameters for given flow capacities.
High molecular weight hydrocarbon soluble polymers such as polyisobutylene, polystyrene, and several poly alpha-olefins have been demonstrated to reduce drag in turbulent flows of hydrocarbon liquids. Generally, the drag reduction effectiveness of these polymers improves with increasing molecular weight; however, the tendency for the polymers to permanently degrade via molecular scission within pumps or turbulent pipeflows also increases with increasing polymer molecular weight. This invention discloses efficient drag reduction in hydrocarbon liquids resulting from a novel class of interacting polymers which interact via an acid-base mechanism. For example a copolymer of an alpha-olefin such as 1-octene incorporating a repeat unit containing a carboxylic acid such as 10-undecenoic acid can interact with a styrene-vinyl pyridine copolymer. Such acid-base interacting polymers can provide improved drag reduction via polymeric networks rather than by high molecular weight. Consequently such networks are less sensitive to flow degradation as exemplified in the instant invention.
This invention teaches that an acid-base interacting polymer complex can be effective as a drag-reducing agent for hydrocarbon solutions. Such a system formed by two interacting polymers, one acidic and one basic, can behave like a higher molecular weight polymer which is normally needed for drag reduction. One can, therefore, form a network from polymers that are relatively lower in molecular weight and potentially reduce sensitivity to backbone degradation under flow. Moreover, the network can be destroyed by adding a small amount of a polar cosolvent additive, such as an alcohol or other polar additives, which is strongly interfering with the interaction mechanism.
We note that high molecular weight polymeric materials in general, are considered useful as drag reduction agents when dissolved in an appropriate solvent system. The major reason for this reduction in fluid drag is due in large part to the very large dimensions of the individual polymer chain as compared to the dimension of the single solvent molecules. Any increase in size of the polymer chain will produce a corresponding enhancement in the drag reduction. This effect is maximized, when the polymer is dissolved in a "good" solvent. Therefore, in general, a hydrocarbon soluble polymer is useful in hydrocarbon solvents while a water soluble polymer is appropriate in aqueous systems.